This document provides an overview of CAN BUS systems used in automotive applications. It discusses the requirements for CAN BUS, including the use of twisted pair cable and termination resistors. The document describes the CAN frame format, including the arbitration, control, data, and CRC fields. It explains the OSI layers for CAN, including the physical layer that transmits electrical signals and the data link layer that handles carrier sensing and collision avoidance. Advantages of CAN BUS are its support for multiple masters, reduced wiring complexity, error detection capabilities, and high speeds up to 1Mbps. CAN BUS is also compared to FlexRay, with CAN having lower cost but lower maximum speed.

1. Raziuddin khazi
Chemnitz University of Technology
Embedded Systems
Second Semester
CAN BUS in
Automotive systems

2. 2
Contents
2
• Introduction
• CAN requirements
• CAN frame format
• CAN OSI layers
 Physical layer
 Data link layer
• Advantages
• CAN vs Flexrays
• References
• CAN bit stuffing

3. 3
Introduction
• CAN was dedicatedly developed for automobile in the 1980’s, today CAN
chips are manufactured by Motorola, Intel, Phillips etc.
• Half duplex, Message based protocol that overtook Ethernet and USB
because of its price to performance ratio & simple hardware.
• ISO-11898 is the CAN standard, CAN2.0A – 11 bit identifier and CAN2.0B
-29 bit identifier.
• High speed CAN - 1Mbps(suspension , engine control ) and Low speed
CAN – 125kbps(power window, wiper control).
Continued..

4. 4
Introduction
Source: http://processors.wiki.ti.com
Typical CAN bus

5. 5
CAN requirements
• Twisted pair cable eliminate the electromagnetic interference.
• Recommended to have maximum 30 nodes with 120 ohm termination .
• According to the ‘rule of thumb’, signal rate * length <= 50
Bus length in
meters
Signal rate in
Mbps
40 1
100 0.5
500 0.10
1000 0.05
Source : www.esp elecrtonics.comSource : http://digital.ni.com

6. 6
CAN frame format
Arbitration : When multiple nodes access the bus same time, the node
with least arbitration wins.
RTR : When RTR = ‘1’ then it is remote frame, otherwise data frame.
IDE : Select standard CAN when ‘0’ and extended CAN when ‘1’
Source: https://en.wikipedia.org
Continued..

7. 7
CAN frame format
Source: http://canbus.pl
Continued..

8. 8
CAN frame format
• DLC: Data length code(4 bits) contains number of bytes of data being transmitted.
• DATA: up to 64 bits (8 bytes) of data can be transmitted.
• CRC: 16 bit cyclic redundancy check detects the transmission error.
• ACK: Dominant bit(0) after receiving correct data, otherwise writes recessive bit(1).
• EOF: Marks the end of frame and disable the bit stuffing .
• IFS: Inter frame space is the time required to move correctly received frame to
message buffer area.

9. 9
CAN bit stuffing
Stuff error:
Active error:
• It has six ‘0’s & eight ‘1’s, For every active error count increments by 8 and rest all
receiving nodes increments by 1.
Passive error:
• Do not block bus traffic but keeps counting, if count is beyond 256 it results into bus
off error.
Bus off error:
• Internally disconnects the node and only re-initialization can solve the issue.
Bit stuffing :
• Transmitter adds the opposite level bit on detecting 5 consecutive same level bits,
and receiver discard the stuffed bit when receiving.

10. 10
CAN OSI : Physical layer
• Physical layer can only be implemented on hardware.
• When transmitting it converts 1’s and 0’s into electrical signal and back again to
bits when receiving.
Source: http://www.ti.com/product/SN65HVD231/datasheet
Continued..

11. 11
CAN OSI : Datalink layer
• It can be implemented both on hardware and software.
• Carrier Sense: Nodes checks the bus status, if the bus is idle then accesses it
otherwise wait.
• Multiple Access/CD+ AMP: Avoid collision when multiple nodes access the bus
same time.
CSMA/CD+AMP explained Source: http://canbus.pl

12. 12
Advantages
• CAN is multi master capable communication.
• Reduce the wiring complexity between nodes.
.
• Error detection and correction capability.
• Easy interface with other protocol.
• High speed up to 1Mbps .
Source: www.ixxat.com

13. 13
CAN vs Flex ray
Properties CAN bus Flex ray
Standard ISO-11898 ISO-17458
Max speed 1 Mbps 10 Mbps
Topology Bus Bus and Star
Cost Low High
Source : https://en.wikipedia.org/

14. 14
References
[1] Controller area network and its applications , Akshay Rane, Ajit schendge,
Volume 4, Issue 3 March 2014.
[2] A novel bit stuffing technique for controller area network(CAN) protocol,
Tapas ranjan, Ayas kant and kamala kant , 978-1-4799-2206-2/14, 2014
[3] Introduction to controller area network by Texas Instruments
http://www.ti.com/lit/an/sloa101b/sloa101b.pdf (accessed on 8-06-2017)
[4] CAN hardware software manual by National instruments
http://www.ni.com/pdf/manuals/370289g.pdf (accessed on 8-06-2017)
[5] http://hem.bredband.net/stafni/developer/CAN.htm (accessed on 6-06-2017)
[6] https://www.kvaser.com/about-can/the-can-protocol/can-physical-layers/
(accessed on 6-06-2017)

15. THANK YOU